This invention relates to centrifugal fans which are used for a variety of purposes to provide an air flow.
Centrifugal fans have been known and used for a considerable length of time. Generally they comprise a rotor with a number of impellers or blades mounted in a housing having an inlet for incoming air and an outlet through which the air is driven. The rotor is rigidly mounted to the end of a driveshaft which is turned by a suitable motor. The fan inlet extends through the side of the housing along the axial centre line of the rotor. Generally in known centrifugal fans the outlet or discharge has a centre line which is parallel to a tangent to the circumference of the rotor, which outlet is formed in the circumferential side of the housing. Because of this arrangement, the fan wheel or rotor must rotate in a direction specified by the outlet arrangement. This in effect doubles the size of the inventory that must be maintained in order to provide centrifugal fans that rotate either counter clockwise or clockwise. Although fan "handing" is achievable by conventional means with this type of fan, rotation modification to an existing unit is not achievable.
In order to produce the known centrifugal fan housings from a plastics material, it is necessary to have two separate moulding units, one for each of the two halves that make up the housing. This requirement arises from a fact that the two halves are not identical, particularly when the centre line of the outlet is parallel to a tangent of the rotor circumference. As these moulds are reasonably expensive, it is desirable, if possible to construct the fan housing using identical mould halves and the present invention permits such a construction.
U.S. Pat. No. 3,797,961 which issued Mar. 19, 1974 to H. Brechbuhl describes a centrifugal fan having a rotor rotated by a driveshaft which extends through the side of the housing. The rotor is made from a plastics material and is connected at the side to a support plate which is connected to the driveshaft. The housing is made of three detachable portions including two side portions and a peripheral housing portion. A large inlet opening is formed in one of the side portions, this being in the portion opposite the driveshaft side. A fan outlet is formed in the peripheral housing portion.
Earlier U.S. Pat. No. 3,301,472 issued Jan. 31, 1967 to American Radiator & Standard Sanitary Corporation describes a blower for moving air which has a scroll or housing 12 and a blower wheel. The blower is of the centrifugal type and is made with two parts, one of which is a substantially flat plate. The other part is made from moulded plastic. The peripheral walls are arcuate and preferably have spiral projections. The axial width of the peripheral walls smoothly and continuously increases along the arcuate direction towards the outlet. The blower wheel is an integral structure including an axial or hub portion and a plurality of vane portions radially extending from the axial portion. Each vane includes a pair of blades that laterally extend from the vane plane.
It is an object of the present invention to provide a simple and relatively inexpensive construction for a centrifugal fan and one which permits the direction of rotation of the fan to be in either direction while using the same fan housing components.
It is another object of the invention to provide a centrifugal fan wherein the fan outlet formed by the housing has a centre line which is located generally on a radius extending from the axial centre of the fan wheel. This results in the centre line of the outlet being in the same plane as the centre line of the axial inlet for the fan. With such an arrangement, the design and construction of air duct systems employing fans of this type is easier.